Compositions for high power piezoelectric ceramics

This application is a continuation-in-part of U.S. patent application Ser. No. 11/104,374, filed Apr. 11, 2005, which is incorporated herein by reference in its entirety.

The present invention relates generally to piezoelectric ceramic compositions, articles formed from these compositions, and to methods for preparing the piezoelectric ceramic compositions and articles.

Piezoelectric elements are widely used in a variety of electronic components including ceramic resonators, ceramic filters, piezoelectric displacement elements, buzzers, transducers, ultrasonic receivers and ultrasonic generators, etc. As a result of the increased demand for piezoelectric elements, there is an increasing use of piezoelectric ceramic compositions to form the elements. There is a drive towards increasingly smaller electronic components, causing an increased demand for smaller piezoelectric elements for use in these electronic components.

However, many of the smaller electronic components require that the piezoelectric elements provide the same or even greater output power, despite their reduced size. The different uses or applications require different electromechanical characteristics from the piezoelectric ceramics. In order for piezoelectric ceramic elements to be used in high power applications, they must exhibit certain characteristics, including high mechanical quality factor (Q_m), a high relative dielectric constant (∈), and a high coercive field (E_c). Additionally, the dielectric loss factor (tan δ) must be sufficiently low to minimize internal heating effects.

Existing high power piezoelectric ceramics often do not exhibit suitable electromechanical properties for use in miniaturized electronic devices. In the current state of the art, the existing piezoelectric elements that are sufficiently small to be used in the miniaturized devices exhibit low capacitance and high electrical impedance. This is inadequate to drive the miniaturized devices. Additionally, if the permittivity is high, the dielectric loss factor (tan δ) of current piezoelectric elements is also high—resulting in internal heating and dissipative loss which significantly decreases the efficiency and output of the device. Consequently, existing piezoelectric ceramics have not provided adequate electromechanical properties for these miniaturized electronic devices.

The electromechanical properties of the piezoelectric ceramics can be altered by varying the specific ceramic composition, the molecular structure, and/or the methods and parameters for fabricating the piezoelectric ceramic.

In light of the above problems, there is a continuing need for advances in the relevant field including new piezoelectric ceramic compositions and piezoelectric elements formed from the compositions. The present invention addresses that need and provides a wide variety of benefits and advantages.

Briefly describing one aspect of the present invention, there is provided a class of ceramic compositions illustrated by Formula 1 below:

Pb_(1-z)M_z(Mn_1/3Sb_2/3)_x(Zr_yTi_1-y)_1-xO₃  (1)

wherein M is selected to be either Sr or Ba, x is selected to be between 0.01 and 0.1, y is selected to be between 0.35 and 0.55, and z is selected to be between 0.01 and 0.10.

In some embodiment of the above composition, one or more dopants are added to the compositions. The dopants may be selected from the group comprising: PbO, SnO₂, Sm₂O₃, TeO₂, MoO₃, Nb₂O₅, SiO₂, CuO, CdO, HfO₂, Pr₂O₃, and mixtures thereof. The dopants can be added to the ceramic composition in individual amounts ranging from 0.01 wt % to up to 5.0 wt %.

The preferred ceramic compositions of the present invention exhibit suitable electromechanical properties for use as piezoelectric elements in high power applications. The preferred piezoelectric ceramics of the invention exhibit one or more of the following electromechanical properties: a relative dielectric constant (∈) of between 1200 and 2000, a mechanical quality factor (Q_m) of between 1500 and 2800; a piezoelectric strain constant (d₃₃) of between 250-450 pC/N, a dielectric loss factor (tan δ) of between 0.002-0.008 and a thickness electromechanical coupling coefficient (k_t) of between 0.45 and 0.7. In some embodiments the ceramic has a relative dielectric constant (∈) of about 1500, a mechanical quality factor (Q_m) of about 2000, a piezoelectric strain constant (d₃₃) of about 350 pC/N, and a dielectric loss factor (tan δ) of less than about 0.004.

It is an object of the present invention to provide high power piezoelectric ceramics.

Further objects, features, aspects, forms, advantages, and benefits shall become apparent from the description and drawings contained herein.